Posted: Fri Jan 11, 2013 12:58 am Post subject:
Ground prong missing from power plug (Yamaha CS-5)Subject description: Can I still use it? What are the risks?

So I have this Yamaha CS-5 synth and I have concerns about the plug as it seems to be missing something (ground prong?). It seems to be the kind that should have three prongs (ground and the other two), but the ground prong was missing and oddly enough both power prongs are the same size (not fat/slim). I haven't seen that before on a three prong plug. I have all my gear plugged in a surge protected power strip and the synth seems to work fine that way but I'm still having concerns about it knowing that ground prongs are there for a reason if that thing ever had one. Can I continue to power the synth this way since it's plugged in a surge protected source or should I keep it unplugged until the plug has been replaced? Any suggestions?

This earth pin has two functions:
It references the ground of the electronic circuit to the same level than the other devices of your studio, the earth.
It provides safeness. For example, the front panels, if they are conductive, must be connected to the earth pin. In this way, if ever, accidentally, a cable with mains electricity touches this front-panel it will be shorted to earth.

That's all I needed to hear. I'll get one from the nearest ACE store tomorrow. Just one more question though - are there any replacement plugs around that don't require to be soldered? My soldering skills are, let's just say sub par.

Ok, fixed it, and it works! Now I have one more question about the synth itself - is the any way to frequency-modulate the filter by utilizing any of the cv/gate inputs? maybe my routing the output to CV or EXT IN and fine tune the trigger level? Or would this result in some kind of FM feedback mess?

Nope, but from what I remember (I'm not at home right now) the rear has ports for External In, trigger in/out, CV in/out and Output. On the upper left part of the front panel is a small section where you can dial in the trigger level and select between Ext. In and Noise. That's all I can tell for now.

Accordingly the block diagram, the control CV affects both, the oscillator and the filter, thus I don't think that it will be very useful for audio modulation.
Furthermore, the response of the control CV in is 0.125V to 4V so the negative part of the wave will not get response.

The chip is fed with a +/-15V power supply and you can guess that it could stand inputs up those values, but we don't know for sure. In the schematics you can not see any input protection. Maybe is a simplified schematic.
The chip must be very difficult to achieve if you damage it.

I would use it only for what it was designed and I would avoid any experiments._________________electronic-sea.net

Interesting. I do agree about using the synth's features as intended, however I found out about a neat trick where you use an audio splitter to route the output back into ext in and get some wild filter feedback out of it. I was wondering if that trick would work with routing the output to CV IN, hence the question in the first place. Thanks for your advice, having a lot of fun with the synth so far.

Update: I sold the CS-5 and purchased a CS-15 locally, and that one also had the ground prong missing. CS-5 I used to have ages ago (before the one I now sold) also had the grounding prong missing but at the time it didnt't seem odd to me because I just didn't know better (and didn't know of electro-music.com either). Were those really that notorious for breaking off or do people remove them for some reason? I don't understand why I get three Yamaha CS synths with missing ground prongs but all my other synths were just fine

There are a lot of electrical products which are not made with a ground connection. Usually because the PSU is "double insulated" or words to that effect. If they have CV and/or Gate in/outputs, the earth may have been omitted from the design in order to guarantee that there would be no "earth loop" problems. If it came from the factory like that then the PSU must have passed an extra level of safety standard, and there should be no problem.
The best way to know for sure is to open it up and see if the earth wire in the mains lead, (assuming there is one) actually connects to anything. Does it use an IEC (D type) power cord? You might find that the earth pin is unconnected inside the chassis, in which case it's not supposed to be earthed, and that's fine.
I hope all that makes sense. _________________What makes a space ours, is what we put there, and what we do there.

I threw away the original plug but in all cases the there was a hole where the ground pin should have been, and the cable actuallly had a ground wire in it, so I'm assuming that there should have been a ground pin on the plug in the first place? As you might have guessed by now the plug is the kind with two flat prongs and a round ground pin above them. I didn't get to check that inside the synth yet tho. What struck me odd was that the flat pins were both equal in size, not wide/narrow, so kind of like they would be on old groundless plug. Well it works fine the way it is, but why three in a row with ground pin missing? Did anyone else get that too? What about other models (CS 5-80, SY 1,2?)

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